Abstract: For x-ray tube potentials larger than 100 kV, the AAPM TG-61 protocol for 40-300 kV x-ray beam dosimetry in radiotherapy recommends an in-water measurement which is based on ionization chambers calibrated in air in terms of air kerma. We studied the variation of the overall correction factor (PQch) and its components (known as corrections for the change in the chamber response due to the change in the spectrum distribution in phantom compared to that used for the calibration in air (kQ), displacement of water by the ionization chamber (Pdis) and displacement of water by the stem (Pstem)) as well as the correction for a waterproofing sleeve (Psheath) with depth and field size for 6 different beam qualities in the orthovoltage x-ray range (100 kV < tube potential < 300 kV).

2. "Searching for hidden patterns in cancer and cardiovascular images"

Rebecca Thornhill –The Ottawa Hospital

Abstract:Conventionally, radiologists produce diagnoses on the basis of a combination of their training, experience, and individual judgment. Radiologists perceive image patterns and associate or infer a diagnosis consistent with those patterns. However, there will be an inevitable degree of variability in image interpretation as long as it relies primarily on human visual perception. Pattern analysis can provide a quantitative vocabulary for the otherwise subjective characteristics of lesions. Tools for automated pattern recognition can provide objective information to support clinical decision-making and may serve to reduce variability. To date we have applied quantitative shape and texture pattern analysis to a number of cancer and cardiovascular imaging applications. Several of these will be discussed, with particular focus on how pattern analysis can supplement conventional radiologic interpretation. Finally, these applications will also provide opportunities to discuss some of the pitfalls and challenges presented by these techniques.

* We will be finishing off this season's seminar series with a BBQ at the NRC. To help in organizing this, we would like to have an idea of how many people are planning to come to the seminar and stay for the food afterwards. Please contact Bryan [dot] Muirnrc-cnrc [dot] gc [dot] ca by May 25 to guarantee your share. We will make every effort to accommodate special dietary needs (e.g. vegetarians) but only if we know in advance.